Oven base insulation

[pizzahead]

Hi. I have a 40mm (bit less than 2") calsium silicate insulation board for underneath the oven floor. Does anyone think that this is not enough insulation. The board is sitting on a concrete hearth 100mm (bit more than 4") thick.

Thanks
Jase

[asudavew]

Re: Oven base insulation

I used vermcrete, but I think you need at least 2 inches of cal sil

You could use a couple inches of vermcrete and then the cal sil board.

Don't skimp here my friend. The more insulation under the floor the better.

Dave

[james]

Re: Oven base insulation

I'll agree with that. The thermal calculations show that 2" of ceramic insulating board (Cal Sil or Alu Sil) is a little better than 4" of vermiculite concrete. The 2" thickness takes a 1000?F face down to something reasonable at equilibrium -- which works well for a home brick oven that will operate for hours at a time, rather than continuously.

If cost isn't too big of an issue, go thicker.

James

[pizzahead]

Re: Oven base insulation

Thanks for the advice. Actually 40mm is a bit less than 2" not 1" - is it still worth laying down maybe 2" of vermiculite/cement? That would mean I would have 40mm cal sil board & 50mm vermiculite/concrete?

Cheers
Jase

[james]

Re: Oven base insulation

Hey Jase,

.393 x 4.0 = 1.572". I should have caught that. :-)

If you lay down 2" of vermiculite concrete under your Cal Sil board, you will be in good shape. That would not be expensive, and not require too much effort.

Nice idea.
James

[pizzahead]

Re: Oven base insulation

Thanks James. Purchased the materials at lunch today and will lay it tonight. How long should I wait for it to cure before I lay out the Cal Sil board and base for the oven?

Also the mix is 5 parts vermiculite to 1 part portland cement, roughly how much water is needed to get a good mix.

Thanks again.

Jase

[james]

Re: Oven base insulation

Jase,

You can do it by sight and feel. Think oatmeal; Scottish oats. You can set your boards on the damp vermiculite concrete, and let it all cure. The boards are light and will not sink or compress the vermiculite.

If you give that a day or two to set, you should be fine.

Would other builders agree with that?

James

[pizzahead]

Re: Oven base insulation

The boards are very light yes, but how long before I can lay out the firebrick oven base and start the dome do you think?

Thanks again.

Jase

[james]

Re: Oven base insulation

As soon as the vermiculite layer is dry enough to not compress.
James

[pizzahead]

Re: Oven base insulation

Thanks for your help James. I laid 75mm (bit over 3") of vermiculite concrete last night and it looks good this morning. That plus the 40mm cal sil board and I should have plenty of insulation for my oven.

Cheers
Jase

[Balthazar]

Re: Oven base insulation

I used 100mm thick Hebel blocks. It's aerated concrete with great insulation properties....and no mess! It can even be cut with a hand saw!!!
I paid AUD$4 per block of 600mm x 200mm x 100 mm. I used 14 blocks for a area of 1200mm x 1400mm.

[pizzahead]

Re: Oven base insulation

Nice idea. Cheap and easy to handle as well. I have already laid the vermiculite witht the Cal Sil boards on top. How did you find out about the insulative properties in Heable blocks? I have seen them at hardware stores but not thought of them for insulation.
Cheers
Jase

[Balthazar]

Re: Oven base insulation

Nice idea. Cheap and easy to handle as well. I have already laid the vermiculite witht the Cal Sil boards on top. How did you find out about the insulative properties in Heable blocks? I have seen them at hardware stores but not thought of them for insulation.
Cheers
Jase

A few friends told me about them, and then I checked out their website:
Hebel : About Hebel

".....It has a unique combination of thermal mass and insulation...."

[mikew]

Re: Oven base insulation

I'll agree with that. The thermal calculations show that 2" of ceramic insulating board (Cal Sil or Alu Sil) is a little better than 4" of vermiculite concrete. The 2" thickness takes a 1000?F face down to something reasonable at equilibrium -- which works well for a home brick oven that will operate for hours at a time, rather than continuously.

If cost isn't too big of an issue, go thicker.

James

I am at the stage of biulding the dome for a 42" oven and was going to use 40mm calsil board directly on the concrete hearth - maybe i will need to add an extra 1" thick calsil layer. would this be adequate ??

Mike

[pizzahead]

Re: Oven base insulation

Hi Mike. I would use more than the 40mm cal sil board. I ended up putting 75mm of vermiculite concrete underneath the 40mm board on my 42" oven and it seems to have worked very well.

Remember, once the dome is built you cannot go back and put more insulation underneath it. It is worth overdoing it now rahter than wishing you had have done it later down the track.

Good luck.
Jase